With regard to a liquid crystal, diverse applications to various kinds of optical elements such as a retardation plate and a polarizing plate except a liquid crystal display element have been studied by utilizing an alignment property and anisotropy of physical properties such as refractive index, dielectric constant and magnetic susceptibility.
An alignment layer is used for aligning a liquid crystal. A rubbing method and a photo-alignment method are known as examples of a formation method for an alignment layer, and the photo-alignment method is useful in view of being capable of controlling quantitative alignment treatment by reason of no occurrence of static electricity and dust as a problem of the rubbing method (refer to Patent Document 1, for example).
Thermal stability and solvent resistance except liquid crystal alignment ability are required for an alignment layer. For example, the alignment layer is occasionally exposed to heat and solvents in the production process of various kinds of devices, and to high temperature during the use of various kinds of devices. The exposure of the alignment layer to high temperature brings a possibility of remarkably deteriorating liquid crystal alignment ability.
Then, for example, in Patent Document 2, in order to obtain stable liquid crystal alignment ability, a liquid crystal alignment agent containing a polymer component having a structure capable of a cross-inking reaction by light and a structure which cross-links by heat, and a liquid crystal alignment agent containing a polymer component having a structure capable of a cross-inking reaction by light and a compound having a structure which cross-links by heat are proposed.
Also, in Patent Document 3, in order to obtain excellent liquid crystal alignment ability, sufficient thermal stability, high solvent resistance and high transparency, a thermosetting film forming composition having a photo-alignment property, containing (A) an acrylic copolymer having a photo-dimerization site and a thermal cross-linking site and (B) a cross-linking agent, is proposed. (B) The cross-linking agent bonds to a thermal cross-linking site of (A) the acrylic copolymer, and the thermosetting film forming composition having a photo-alignment property is cured by heating to form a cured film, and then an alignment layer may be formed by irradiating the cured film with polarized ultraviolet rays.
In Patent Document 4, in order to obtain excellent liquid crystal alignment ability, sufficient thermal stability, high solvent resistance and high transparency, a thermosetting film forming composition having a photo-alignment property, containing (A) an acrylic copolymer having a photo-dimerization site and a thermal cross-linking site, (B) an acrylic polymer having at least one of predetermined alkyl ester group and hydroxyalkyl ester group, and at least one of a carboxyl group and a phenolic hydroxy group, and (C) a cross-linking agent, is proposed. (C) The cross-linking agent bonds to a thermal cross-linking site of (A) the acrylic copolymer and to a carboxyl group and a phenolic hydroxy group of (B) the acrylic polymer, and the thermosetting film forming composition having a photo-alignment property is cured by heating to form a cured film, and then an alignment layer may be formed by irradiating the cured film with polarized ultraviolet rays.
In Patent Document 5, in order to obtain excellent liquid crystal alignment ability, sufficient thermal stability, high solvent resistance and high transparency, a thermosetting film forming composition having a photo-alignment property, containing (A) a compound having a photo-alignment group and a hydroxy group, (B) a polymer having at least one of a hydroxy group and a carboxyl group, and (C) a cross-linking agent, is proposed. (C) The cross-linking agent bonds to a hydroxy group of (A) the compound and to a hydroxy group and a carboxyl group of (B) the polymer, and the thermosetting film forming composition having a photo-alignment property is cured by heating to form a cured film, and then an alignment layer may be formed by irradiating the cured film with polarized ultraviolet rays.
Also, in Patent Document 6, a composition for a photo alignment film containing an azo compound having a polymerizable functional group is disclosed. The composition for a photo alignment film may be polymerized by light or heat.
In Patent Document 7, a copolymer being a cross-linkable photoactive polymer comprising (a) at least one monomer from the group of acrylate, methacrylate, acrylamide, and methacrylamide, in which photochemically isomerizable molecules or dimerizable molecules are bonded covalently or directly, or bonded via a cross-linking group, (b) at least one comonomer containing a hydroxy group, and (c) another ethylenically unsaturated comonomer as the case may be, is disclosed. The copolymer may be polymerized by light or heat.